Chair base



FIG. 1 is a top perspective view of a chair base illustrating the design;

FIG. 2 is a bottom perspective view of the chair base;

FIG. 3 is a left side view of the chair base, the right side being a mirror image thereof;

FIG. 4 is a front view of the chair base;

FIG. 5 is a rear view of the chair base;

FIG. 6 is a top view of the chair base; and,

FIG. 7 is a bottom view of the chair base.

The right hand side view of the chair base is as illustrated by FIG. 3.

The portions of the chair base shown in dashed lines do not form part of the design.

The broken lines in the drawings represent unclaimed environmental subject matter. 

The ornamental design for a chair base, as shown and described. 